Not applicable
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I. Field of the Invention
The present invention relates to an ear-worn device that is comprised of a soft yet solid elastomer corpus for use in custom in-the-ear hearing products. The degree of stiffness of this soft-solid material preferably ranges from negligible to forty points, Durometer Hardness, Shore A. Specifically, the present invention relates to a system and method for producing a custom soft yet solid elastomer hearing product yielding greater comfort and superior acoustic performance for the hearing instrument wearer. Additionally, this product will provide solutions to a population with whom traditional custom in-the-ear technology was unsuccessful. By the nature of its soft design this product will have improved compliance and elasticity, thereby better accommodating the dynamic nature and the anatomical variants of the external ear canal. This invention will also relate to future applications in the field of mass communications, such as an ear-worn digital telephone or a two-way radio system.
II. General Background of the Invention
The Hearing Instrument Industry combines electro-acoustic technology with custom prosthetic design to ergonomically couple a hearing instrument to the human ear in a cosmetically acceptable manner. The industry has realized major electronic advancements in hearing instrument technology. With miniaturization of electronic components the standard instrument design evolved from a table worn unit, using vacuum tubes in the nineteen twenties, to a wearable body worn unit in the late nineteen thirties. The introduction of transistors in the nineteen fifties made the behind-the-ear (BTE) hearing instrument possible. As integrated circuits were developed, the custom in-the-ear (ITE) instrument became a reality. On-going electronic developments surrounding the hearing instrument industry have resulted in the micro-miniaturization of electronic components. This miniaturization has culminated in the introduction of xe2x80x9cdeep insertion technologyxe2x80x9d, manifested as the completely-in-the-canal (CIC) hearing instrument, which is totally contained within the ear canal and is virtually invisible. As a consequence, hearing instruments have increased signal processing capabilities, yet require very limited physical space.
With the development of programmable hearing instruments, using either analog or digital signal processing, custom electronic design has shifted from the manufacturing level to the clinical level. That is, the clinician can now customize the electro-acoustic response of the instrument to match the degree of hearing loss via programmable software. It is no longer necessary for the device to be returned to the manufacturer for hardware changes to achieve the desired electro-acoustic characteristics.
In direct contrast to electronic advances within the industry, little or no advancement has been realized in custom prosthetic design. Since the late nineteen sixties, when the custom instruments were developed, the materials and the construction techniques have remained virtually unchanged. These materials and techniques were adopted from the dental industry, whereby the customized housingxe2x80x94commonly called a xe2x80x9cshellxe2x80x9dxe2x80x94was constructed using acrylic with a ninety point xe2x80x9cDxe2x80x9d Shore Hardness. Typical molding of the dental acrylate involves making a female silicone cavity from the original ear impression. This female cavity is then filled with liquid acrylate and cured using an ultraviolet light of known intensity across a known time period to cure only the outer most material forming a wall or a shell. This process is very similar to ceramics. The shell is then removed from the female cavity, decked down in the sagittal plane, drilled for vents and receiver bores, polished and then mounted with a faceplate containing the electro-acoustic circuitry. The end result is a hollow glass-like plastic replica of the external ear canal. The finished shell""s primary function is to house the delicate electronic components. Yet, a material of this hardness, worn deeply in the human ear canal, brings forth the issues of comfort and acoustic performance.
When the acrylic shell was introduced, hearing instruments were worn in a relatively elastic cartilaginous portion of the ear canal. However, the current trend for hearing instrument placement is to position the device into the bony portion of the ear canal extending three millimeters medially from the second directional bend previously defined as xe2x80x9cdeep insertion technologyxe2x80x9d. To illustrate the implications of this technology, the anatomy and physiology of the ear will be reviewed.
Anatomically, the ear canal is defined as the area extending from the concha to the tympanic membrane. It is important to note that the structure of this canal consists of elastic cartilage laterally, and porous bone medially covered by skin. The cartilaginous portion constitutes the outer one third of the ear canal. The medial two-thirds of the ear canal is osseous or bony and is oriented forward and downward making it slightly concave as compared to the more cylindrical cartilaginous portion. The average canal is approximately twenty-five millimeters in length but is as much as six millimeters longer on the anteroinferior wall of the osseous canal. The skin of the osseous canal, measuring only two-tenths of a millimeter (0.2 mm) in thickness, is much thinner than the skin of the cartilaginous canal, measuring five-tenths to one millimeter (0.5 to 1 mm) in thickness. The difference in thickness directly corresponds to the presence of apocrine (ceruminous) and sebaceous glands found only in the fibro-cartilaginous area of the canal. This thinly skinned, thinly lined area of the bony canal is extremely sensitive to any hard foreign body, such as an acrylic hearing instrument.
Physiologically, the ear canal is dynamic in nature. It is geometrically altered by mandibular action and by head position changes. These cause alternating elliptical elongation and widening of the ear canal. These alterations in canal shape vary widely, not only from person to person, but also from ear to ear.
Applying hard, hollow, acrylic hearing instrument technology to the external ear canal has numerous limitations. Because of the rigid nature of the acrylic shell of many traditional instruments, they are difficult to insert beyond the second directional canal bend. The difficulty of insertion is increased in the presence of any anatomical variant such as a stenotic canal, a bulbous canal, or a tortuous canal.
Because of the rigid nature of the acrylic shell of many traditional instruments, they must pivot in reaction to mandibular action or head movement, thereby changing the angle of attack of the receiver toward the tympanic membrane resulting in a distorted acoustic response.
Additionally, this pivoting action often causes displacement of the entire instrument causing a slit leak between the wall of the device and the wall of the ear canal. That leak creates an open acoustic loop between the receiver and the microphone of the instrument resulting in an electro-acoustic distortion commonly known as feedback.
Because of the rigid nature of the acrylic shell, some deeply inserted traditional instruments will exert pressure upon the bony portion of the ear canal when mandibular action or head movement cause the instrument to pivot.
Because of the hollow nature of the acrylic shell, many traditional instruments cannot protect the internal components from damage due to shock (i.e. the impact suffered by a traditional instrument dropped onto a hard surface).
Because of the hollow nature of the acrylic shell, many traditional instruments provide an air-conducted feedback loop from the receiver to the microphone.
Because of the hollow nature of the acrylic shell and the inherent necessity to suspend the receiver by tube mounting, the traditional instrument is prone to collection of cerumen in the receiver tube. Attempts to excavate the cerumen often breaks the bond between the receiver tube and the receiver port of the shell, displacing the receiver into the instrument.
Because of the solid nature of the acrylic shell, the proximal tip of many traditional instruments serves as a reverberating surface for acoustic energy reflected by the tympanic membrane resulting in distortion.
Because of the rigid and hollow nature of the acrylic shell, traditional instruments with such a shell have relatively widely separated interior surfaces that promote internal acoustic reverberation and its attendant feedback.
To compensate for these limitations, modification to the hard shell exterior to approximate the anatomical variants and to meet the demands of the dynamic nature of the ear canal are performed. The shell is buffed and polished until comfort is acceptable without significantly compromising acoustic performance. The peripheral acoustic leakage caused by these modifications often results in acoustic feedback (whistling) before sufficient amplification can be attained. Additionally, this acoustic leakage causes annoying low frequency sounds to be inadvertently amplified by means of a Helmholtz resonator. Patients commonly report this sensation as xe2x80x9cMy voice is hollowxe2x80x9d or xe2x80x9cMy head sounds like it is in a barrel.xe2x80x9d
Another approach taken to compensate for the limitations of the hard, hollow acrylic shell has been to alter the electro-acoustic parameters of the instruments. It was expected that, with the development of programmable devices, a sophisticated, precise electro-acoustical method of eliminating these acoustic anomalies would be available to the clinician. Ironically, the improved frequency spectrum of the programmable instruments exacerbated the problem. The practical solution was to adjust the program of an instrument which was exhibiting feedback by reducing the high frequency information, or to retreat to a larger behind-the-ear hearing aid.
Faced with the limited success of shell or electro-acoustic modification, a few manufacturers have attempted all-soft shells. Wearers did report greater comfort and better sound quality. Unfortunately, while rigid acrylic does not lose its dimensional stability, soft vinyl materials shrink, discolor, and harden after a relatively short period of wear (the replacement of vinyl material used for BTE earmolds, for example, is recommended on at least a yearly basis). Polyurethane provides a better acoustic seal than polyvinyl, but has an even shorter wear life (approximately three months). Silicones have a long wear life but are difficult to bond to plastics, a necessary process for the construction of custom hearing instruments. Furthermore, silicone is difficult to modify when the dimensional structure requires alteration for proper fit. To date, then, acrylic has proven to be the only material with long term structural integrity. The fact remains, however, that the entire ear is a dynamic acoustic environment ill-served by a rigid material such as acrylic.
Some references of interest are discussed below. These references are all incorporated herein by reference.
U.S. Pat. No. 4,870,688 to Voroba, Barry, et al.
Voroba describes a patient selected mass produced, non-custom molded form fitting shell with a malleable covering having a hook and twist which in theory precisely conforms to the patient""s own ear.
U.S. Pat. No. 4,880,076 to Ahlberg, Carl, et al.
Ahlberg discloses a user-disposable foam sleeve comprising a soft polymeric retarded recovery foam that can be compressed to be freely inserted into the patient""s ear and then allowed to expand until secure in the ear canal.
Other patents that may be of interest include the following:
U.S. Pat. No. 5,002,151 to Oliveira, Robert J., et al.;
U.S. Pat. No. 4,607,720 HEARING AID;
U.S. Pat. No. 4,375,016 VENTED EAR TIP FOR HEARING AID AND ADAPTER COUPLER THEREFOR;
U.S. Patent Nos.: 4,051,330; 4,716,985; 4,811,402; 4,937,876; 5,068,902; 5,185,802; 5,201,007; 5,259,032; 5,530,763; 5,430,801; 5,500,902; and 5,659,621.
Also of interest and incorporated herein by reference are published Japanese patent application no. JA61-238198, the articles from December 1997 JOURNAL OF AMERICAN ACADEMY OF AUDIOLOGY, and Staab, Wayne J. and Barry Finlay, xe2x80x9cA fitting rationale for deep fitting canal hearing instrumentsxe2x80x9d, HEARING INSTRUMENTS, Vol. 42, No. 1, 1991, pp. 7-10, 48.
The present invention relates generally to in-the-ear hearing aids and particularly to a soft elastomer solid within which the electronic components are embedded. The hearing aids can be custom or mass produced. The general objective of this invention is to provide a product which is authentic to the shape of the external ear canal, yet compliant enough to compensate for the dynamic properties of the canal. In addition to that general objective, there are specific objectives. This objective is accomplished by providing a body which, in the preferred embodiment of the present invention, has a 5-15 durometer, Shore A hardness to optimize the following apparently opposing desired characteristics:
the device should be stiff enough to easily insert into the ear;
the device should be soft enough to compress and recover, once inserted into the ear, as the jaw""s mandibular action flexes the external ear canal changing the horizontal diameter as it opens and closes; and
the device should not tear or elongate during stretching to the point that the strain relief systems between the amplifier and receiver would be overly burdened to failure. i.e. wires or connections would not break when the device is flexed by tensile force, compression, torsion or a complex combination of the three forces.
The present invention includes an ear-worn hearing device a hearing device body sized and shaped to generally fit into a human ear canal; and an electronic hearing circuit embedded in the body, wherein the body is made of a soft-solid elastomer and the body has a Durometer Hardness, Shore A, of less than 40 points.
The body of the device of the present invention preferably comprises an elastomer blend which once completely vulcanized is bondable to another elastomer blend which has not been vulcanized and which is of similar elastomeric characteristics in the finished and unfinished state, both of which can be formulated at the very low end of the shore A scale (preferably ranging from 0-17 Durometer). This bonding capability will provide a platform for the resizing of an existing device and further provide the platform for the manufacture of a series of universal, non-custom, soft-solid devices. These universal devices could be customized by the manufacturer or at the clinic on a later date using a dipping process or some other external patching technique to bond the existing soft-solid device to a new outer layer of soft-solid elastomer. It is also possible to use this bonding process to bond a soft elastomeric outer layer to a universal shell made of traditional hard, hollow, acrylic shell material (though it would be preferred to fill this shell with elastomer to obtain the benefits of a solid device).
This bonding capability will provide the platform for the manufacture of a soft-solid device of two different designs. The first design would be similar to an MandM brand peanut candy, where the electronic components are the peanut. The inside chocolate would be made of elastomers which are stiff (27 Shore A Durometer, e.g.) to serve as a skeleton support for insertion into the ear. This center medium would be relatively thin compared to the candy, say 2 mm or less. The outer candy shell would be very soft (e.g. 7-10 Shore A Durometer) and would be thick, 3 mm or more as the size dictates.
The second design would be more like the candy model, in that the center would be very soft elastomer (3-10 Shore A Durometer, e.g.) and approximately 3-4 mm in thickness as the ear canal allows and outer shell would be approximately 27 Shore A Durometer, e.g., and for example 1 mm thick. In this design the insertion rigidity would be provided by the outer layer. The components in the inner layer would be embedded in soft elastomer allowing it to move more easily and would not bond the components as tightly reducing the conductive pathways between the receiver and other components.
Both of these approaches would allow the product to be inserted into the ear, maintain wall pressure on the ear canal wall, and allow the components to move with dynamic motion with the aid of a proper wire stain relief system described later herein.
The present invention, because of its soft nature, will not migrate out of the external ear canal with jaw excursion. It is resistant to the lateral migration which is innate to traditional non-compliant shell.
The present invention, by its soft nature, will remain authentic to the topography of the ear canal, and will remain acoustically sealed with jaw excursion. The acoustic seal will reduce the peripheral leakage, and allow for greater gain and sound pressure before feedback. Concomitant with the improved acoustic seal and the elimination of the slit leak, there will be greater mid-frequency amplification and the elimination of high frequency roll-off, thereby emphasizing those frequencies most important for the perception of consonantal cues.
A total of 24 patients (44 ears) have been fit with the soft-solid device for the purpose of pilot investigations and product development. Results of these pilot investigations have shown the device to be more comfortable when compared with standard acrylic instruments. The soft-solid instrument was shown to accommodate the pivotal action of the jaw in that most wearers reported that the hearing aid, once seated, did not need repositioning over the course of the day. In other words, this soft-solid material was found to eliminate the migration of the hearing aid from the ear due to jaw movement. Hearing instrument users with a history of excessive feedback reported a reduction in feedback when using the soft-solid devices. For some wearers, feedback was entirely eliminated when using a soft-solid device. Finally, pilot investigations found the soft-solid instrument appropriate for patients with bulbous, tortuous, or surgically altered ear canals.
In addition to the improvements in fit and comfort, the soft-solid instruments were found to provide more overall gain in the ear canal than acrylic devices due to the reduction of feedback. In other words, patients were able to increase the gain of the hearing aid (via the volume control) more in the soft-solid devices before reaching the point of feedback. This increased utility of gain may allow for a greater fitting range of completely-in-the-canal hearing instruments. Finally, many patients reported improved sound quality and xe2x80x9cdistinctness of soundsxe2x80x9d when comparing the soft-solid devices to acrylic devices. This may be attributed to the finding in the pilot investigations that the soft-solid devices produced greater mid-frequency gain in the real ear compared to an acrylic device with the same 2 cc data.
These preliminary finding of the pilot investigation warrant a controlled clinical trial of the soft-solid hearing device.
The present invention, because of its soft nature, will not exert pressure on the bony portion of the external ear canal making it easily insertable beyond the second anatomical bend. This deeper insertion reduces residual volume between the proximal tip of the instrument and the tympanic membrane. Because sound pressure increases as residual volume decreases, more power is perceived without a corresponding increase in the gain of the instrument.
The present invention, because of its soft nature, will better accommodate anatomic aberrations such as tortuous ear canals, bulbous ear canals, stenotic ear canals, and iatrogenically altered ear canals.
The present invention, because of its solid nature, will protect the embedded electronic components.
The present invention, because of its solid nature, will eliminate the internal air conducted feedback pathway from the receiver to the microphone.
The present invention, because of its solid nature, will eliminate the need to suspend the receiver by tube-mounting, thereby preventing displacement of the receiver within the hearing instrument and eliminating the concomitant Helmholz resonation.
The present invention, because of its soft-solid nature, can be formulated in such a way as that the elastomer can be blended with conductive particles, such as gold dust or ferrite dust, to form a static shield protecting the circuitry from Radio Frequency Interference (RFI), Global System for Mobile Communication (GSM), and Electromagnetic Interference (EMI).
The present invention, because of its solid nature, can support the receiver and associated tubing. Because of its soft nature, the invention is compressible. Therefore, by compressing the tip of the instrument, cerumen can be extruded away from the receiver and out of the receiver port.
The present invention, because of its soft proximal tip, has a less reflective external surface than the traditional acrylic tip, thereby reducing intermodulation and reverberation.
The present invention, because of its solid nature, has no internal reflective surfaces, thereby eliminating internal reflection and reverberation.
The present invention, preferably comprising an elastomer blend at the very low end of the shore A scale (preferably ranging from 0-17 Durometer), will provide a platform for the manufacture of a series of universal, non-custom, soft-solid devices.
The present invention, because of its solid nature, provides for precise, uniform vent diameters, thereby providing predictable electro-acoustic responses.
The present invention, when incorporating a soft faceplate, results in a completely soft hearing instrument.
The present invention, because it is processed by casting a female cavity from the impression, eliminates buffing, waxing, and other means of impression modification inherent to current shell manufacturing procedures. By streamlining the assembly procedure, the present invention is more easy to produce andxe2x80x94consequentlyxe2x80x94less expensive to manufacture than the traditional hard, hollow acrylic shell.
The present invention includes the soft-solid body described herein, even when it is not filled with electronic components.
The present invention will accommodate additional personal communication devices such as telephones, pagers, memo-recorders, and two-way communication devices, instead of or in addition to hearing aids. In some cases (especially when a hearing aid is not included) it will be desirable to not make a good acoustic seal so that the person using the personal communication devices can also easily hear what is around him.
The present invention, because of its solid nature, can accommodate a bladder mounted in the center which can be filled with a soft material while positioned within the human ear canal. While the device remains in the ear canal, the soft center can be allowed to cure to a hardness less than 35 Durometer Hardness, Shore A. Also, the bladder could be used to vary the amount of occlusion by varying the amount of gel present in the bladderxe2x80x94in such a case, there could be a valve to allow filling and evacuation of the bladder. A hypodermic syringe, for example, could be used to fill and evacuate the bladder. The soft material can comprise a gel elastomer or petroleum jelly, for example.
The present invention can be produced with a sufficiently low Durometer (e.g., 3-17) so as to allow sleeping with the instrument in place.
The current preferred embodiment of the invention eliminates the need for modifications of ear impressions, generally accomplished through altering the shape of the impression and waxing the altered impression. Hence, a more direct method of casting is achieved, yielding greater accuracy of topographical detail of the ear canal in terms of dimensional and geometric characteristics.
The preferred embodiment utilizes a material that is a blended silicone that accepts bonding to plastic by adhesives. Other embodiments of the invention may utilize rubbers, elastomers, and other rubber-like materials including neoprene, silicone, vinyl, butyl and soft plastics.
Preferably, the body occupies at least 70% of the volume of the hearing device not occupied by the electronic hearing circuit. More preferably, the body occupies at least 80% of the volume of the hearing device not occupied by the electronic hearing circuit. Even more preferably, the body occupies at least 90% of the volume of the hearing device not occupied by the electronic hearing circuit. Most preferably, the body occupies at least 99% of the volume of the hearing device not occupied by the electronic hearing circuit.
The outer surface of the body of the present invention is preferably non-absorbent and virtually impervious to cerumen.